Nonmagnetic ferronickel-chromium alloys of low thermoelastic coefficient



Jtme 23, 1970 x. WACHE 3,516,823

NONMAGNETIC FERRONICKEL-CHROMIUM ALLOYS I 0F LOW THERMOELASTIC COEFFICIENT Filed July 12. 1967 2 Sheets-Sheet l June 23, 1970 X. WACHE 3,516,823

NONMAGNETIC FERRQNICKEL-CHROMIUM ALLOYS OF LOW THERMOELASTIC COEFFICIENT Filed July 12. 1967 2 Sheets-Sheet 2 United States Patent Oflice Xavier Wach, Sauvigny-les-Boi's, France, assignor to Societe Metallurgique dImphy, Paris, France, a com. pany of France Filed July 12, 1967, Ser. No. 652,771 Claims priority, application6France, July 21, 1966,

Int. Cl. C22c 39/20 Us. or. 75-128 1' Claim ABSTRACT OF THE DISCLOSURE A nonmagnetic'alloy having a zero or approximately zero thermoelastic coeflicient including by weight 26 to 29% nickel and to 8.5% chromium, the remainder being iron and possibly small percentages of carbon, silicon, manganese and tungsten. Balance springs obtained from this alloy are used for watches.

The invention relates to nonmagnetic alloys and bal- "i ance springs made from such alloys.

Four well-known parameters define the qualities of a balance spring: the temperature coefiicient, the coefficient of isochronism, the position variation and the middletemperature error. The temperature coefficient is a fundamental parameter describing the sensitivity of the spring to variations in the ambient temperature. The other three parameters will not be described here, since they are not directly relevant to the invention and are well known to horologists.

The temperature coefficient is a function of the thermoelastic coefficient of the alloy used for making the balance spring, this thermoelastic coefficient characterising the influence of temperature variations on the modulus of elasticity of the alloy.

When a balance spring is made, one aim is to obtain a zero temperature coefiicient, for example by using an alloy having, under the operating conditions of the spring, a zero thermoelastic coefficient.

It is well known, moreover, that ferronickel alloys have an anomalous thermoelastic coefficient which will be explained with reference to the accompanying FIGS. 1 to 3.

FIG. 1 shows, for a temperature of 50 C., the variation in the thermoelastic coefiicient (X10 and more particularly of the apparent temperature coefficient of the portion module as a function of the percentage by weight of nickel in the ferronickel alloys.

FIG. 2 shows, for a ferronickel alloy with 32% nickel, the variation in the thermoelastic coefficient (X10 with temperature.

FIG. 3 is a graph corresponding to that in FIG. 1 for an alloy containing 10% more by weight of chromium.

Certain alloys with a high nickel content have a thermoelastic coeflicient which is definitely positive in certain temperature ranges, although in general the coefficient is negative.

At a given temperature this thermoelastic coeflicient varies considerably according to the nickel content of the alloy. This variation is illustrated by the curve in FIG. 1

3,516,823 Patented June 23, 1970 fornickel contents ranging approximately from 30 to and for a temperature of 50 C.

For a given nickel content, moreover, the thermoelastic coetlicient varies according to the temperature. This second variation is illustrated by the curve in FIG. 2 for an alloy with 25% nickel.

For a given alloy, the thermoelastic anomally correlates with the magnetic transformation at the Curie point. More particularly, the temperature in which the absolute value of the thermoelastic coefficient is zero or very small is generally little different from the Curie point of the alloy.

Because of the existence of this anomaly, the thermoelastic coefficient of some ferronickel alloys is practically zero, and therefore these alloys can in theory be used for making balance springs. However, they have two disadvantages for such use. Firstly, the rapid variation in the thermoelastic coefficient according to the nickel content in the zone corresponding to zero values of this coefficient would requireto give an alloy of given characteristics a precision of manufacture which is not generally pos 'sible in industrial production. This is clear from the curve in'FIG. l where the points with a zero coefficient are points A and B. Also, the mechanical characteristics, more particularly the elastic limit, of these alloys are inadequate.

These two disadvantages can be largely overcome by adding chromium to alloys with a ferronickel base. In particular, the thermoelastic anomaly is attenuated, so that the curve in FIG. 1 assumes the appearance of that in FIG. 3 after only 10% of chromium has been added.

It is therefore possible to define the ranges in the composition of ferronickel chromium alloys which can be produced industrially and which satisfy the requirements for materials from which balance springs are to be made.

An alloy of this type, containing on average, in addition to iron, 32% nickel, 10% chromium, 3.5% tungstem and additions of 0.7% by weight carbon, 0.3% by weight silicon and 1.9% by weight manganese, was produced for use in the clock industry under the name Elinvar (registered trademark belonging to Societe Metallurgiquc dlmphy).

In view of the correlation between the thermoelastic anomaly and the magnetic transformation at the Curie point, it was generally agreed that this type of alloy combined a zero thermoelastic coefficient with fairly marked magnetism. However, while a balance spring made of a material having this combination of features is appropriate for a watch with a mechanical movement, it is not suitable for an electrically operated watch, which requires a balance spring which has a zero temperature coeflicient and is nonmagnetic.

The present invention relates to a considerable improvement to the ferronickel-chromium alloys generally used, and makes these suitable for making balance springs for electrically operated watches.

The applicant has found that, contrary to what was previously thought, ferronickel-chromium alloys with additions of desired quantities of carbon, silicon, manganese, tungsten, could have a zero or approximately zero thermoelastic coefiicient at the ambient temperature at which they are used slightly above or slightly below their Curie point.

The invention consists of'a nonmagnetic ferronickelchromium alloy including by weight26"*to"29% nickel and 5 to 8.5% chromium, the remainder being iron and possibly small percentages of carbon, silicon, manganese and tungsten.

The invention also consists of balance springs obtained from this alloy.

The applicant has tested variouse alloys with a zero or approximately zero thermoelastic coefficient at the ambient temperature, near their Curie point. By way of example, an alloy having the following composition by weight can be cited:

Remainder Fe.

This alloy has all the properties generally required of materials for balance springs. Also, its Curie point, when it has been annealed, is +29 C., i.e., very close to the ambient temperature.

In practice, when used, the alloy is at the lower limit of the nonmagnetic range. It is not attracted to a magnet. A conventional alloy for balance springs, on the other hand, would have a Curie point of approximately 100- 200 C. and would be distinctly attracted to a magnet. 30

In the embodiment considered, the large drop in the Curie point results from a simultaneous and carefully selected reduction in the nickel and chromium contents by comparison with the contents of approximately 32 and it has been found that the nickel and chromium contents "of the newgroup of alloys thus defined must be within the following ranges:

26 to 29% for the nickel 5 to 8.5% for the chromium,

without exceeding the scopeiotthe invention.

What is claimed is:

1. A nonmagnetic "alloy of-approxirnately zero thermoelastic coefiicient-- consisting' essentially by weight, of 27.4% nickel, 5.7% chrorhium, 0.7% carbon, 0.3% silcon, 1.9% manganese and 3.5 tungsten, the remainder being iron.

References- Cited UNITED STATES A E S 1,513,793 11/1924 Armstrong Q 75 128 3,362,855 1/1968 Shimo 75.l28 1,528,478 11/1955 I Mitchel 75-128 2,725,493 3/1925 Hadfield 75-1289 FOREIGN PATENTS 627,981 8/1949 Great Britain.

and 10% respectively usual in the conventional alloy. HYLAND BIZOT, Primary Examiner This reduction is an important feature of the invention, 

